The present invention relates, in general, to a microwave waveguide-to coplanar transmission line adaptor.
Microwaves can be transmitted through a number of different types of transmission media, including waveguides, microstrip transmission lines and coaxial cables. Often times, it is necessary to interface one type of transmission medium with another. Various types of transitions or adaptors have been employed for this purpose which comprise impedance matching structures for interfacing the two types of transmission media to insure that the electric and magnetic field lines of the microwave will match at the interface.
Examples of such impedance matching structures include fins, ridges and steps, that are disposed in a waveguide, and guide microwaves into an interface, which can be with a microstrip transmission line, for example. The ridges, fins and steps are physically designed to transform the impedance of the waveguide to match that of the microstrip transmission line. For example, to match the waveguide impedance to a 50 ohm microstrip, a ridge can be used whose thickness and height is tapered. The actual impedance transition involves the transition from the normally high impedance of the waveguide (on the order of a few hundred ohms) where the ridge height is zero, to the lower 50 ohm impedance of the microstrip where the ridge contacts the microstrip.
To date, microwave transition and adaptor structures have been fairly complicated and costly due to the interfacing and impedance matching requirements. Also, no efficient, broad band adaptors are known which can interface a waveguide to a structure having more than one ground plane. The present invention seeks to provide an adaptor structure which solves these problems.